1. Background of the Invention
The present invention relates to a porous structure used in inter-fluid contact equipment to achieve contact between gases, between liquids or between gas and liquid, for various industrial purposes, such as packed towers for distillation, absorption, cooling and stripping. The invention further relates to a porous structure used for contact between fluid and catalyst.
In the art of such inter-fluid or fluid-catalyst contactors for various industrial applications, different types of packings have been used to fill towers or columns for intended chemical processings. These packings, which are made of ceramics, glass, synthetic resin or metal, are dumped into a tower in random or in an irregular fashion in the form of beads, pellets, rings (cylinders), sheets, and so forth. Alternatively, the packings are arranged in the tower in a regular or stacked fashion in the form of grids or honeycombs. Although the irregular dumping method permits easy filling of the tower with the packings, it suffers a loss of pressure of the fluids flowing through the irregularly dumped packings. In view of this inconvenience, regularly stacked packings in the form of grids, honeycombs, etc. have been dominantly used for recent years, for minimum pressure loss of the fluids, notwithstanding comparatively time-consuming filling of the tower with such regularly stacked packings.
In the case where a tower is filled with known regularly stacked packings of grid or honeycomb type, it is a common practice that the fluid flow channels formed through the packings are generally oriented substantially in parallel to the line of flow of the fluid through the tower. As a result, the pressure loss encountered with this regular arrangement is less than that experienced on pellet-type packings or other irregularly dumped packings. However, the stacked packings suffer a relatively low frequency of collision between liquid and gas, which results in a local blow or channeling of the gas without contacting the liquid, thus reducing the liquid-gas contact efficiency.
Similar inconveniences are also experienced in the case where such packings are used to fill a tower through which a gas or liquid is caused to flow for contact with a catalyst supported on the packings, in order to catalyze such a fluid during its flow through the tower.
In view of the inconveniences described above, H. Masaki, one of the co-inventors of the present invention proposed a porous structure which provides for reduced pressure loss and permits improved efficiency of contact between fluids, as disclosed in U.S. Pat. No. 4,719,090.
The disclosed porous structure through which at least one fluid flows, comprises a plurality of stacked packings, each stacked packing including a plurality of adjacent located honeycomb blocks. Each honeycomb block comprises: (a) a plurality of first partition walls extending in a first direction and having a longitudinal axis, each of the first partition walls being spaced apart from each other in a second direction which is substantially perpendicular to the first direction, and the plurality of first partition walls being in a substantially parallel relationship, and (b) a plurality of second partition walls extending in the second direction, such that each second partition wall contacts two adjacent first partition walls along a substantial length of each of the second partition walls, the second partition walls being spaced apart from each other and being inclined relative to the longitudinal axis of the first partition walls, the first and second partition walls cooperating to form a plurality of inclined parallel channels in each honeycomb block. The adjacently located honeycomb blocks in each of the stacked packings have all longitudinal axis of the first partition walls of each honeycomb block in a substantially parallel relationship with each other and the inclined parallel channels of adjacent honeycomb blocks are inclined with regard to each other, and when the packings are superposed, inclined channels of honeycomb blocks in a first packing communicate with inclined channels of corresponding honeycomb blocks in a second packings in a zigzag manner, thereby forming a plurality of zigzag fluid passages through the porous structure. The second partition walls have perforations formed through the thickness thereof, the inclined parallel channels in each honeycomb block communicating with each other through the perforations.
However, a further investigation by the present inventors revealed a limited efficiency of fluid contact in a porous structure of the type described above. Described more particularly, the porous structure as disclosed in the above-identified U.S. Patent has perforations formed through the second partition walls, so that a fluid or fluids may flow between the adjacent parallel channels through the perforations, in the nominal direction in which a mass of the fluid or fluid as a whole flows through the porous structure. However, the first partition walls extending perpendicularly to the nominal fluid flow direction of the structure have no perforations, and therefore do not permit fluid communications in the direction perpendicular to the nominal fluid flow direction. Further, the porous structure in question does not permit fluid communications between the adjacent honeycomb blocks which are arranged in the direction perpendicular to the nominal fluid flow direction. For these reasons, the improvement in the efficiency of contact between liquids or between a liquid and a gas, that can be offered by the proposed porous structure is more or less limited. Even if the first partition walls are formed with perforations, these perforations merely permit fluid communications between the adjacent parallel channels on both sides of each first partition wall. Since the first partition walls extend parallel to the nominal fluid flow direction of the porous structure, the fluid movements through the perforations in the first partition walls can not be sufficient.